As a conventional example, a fuel injection valve of a fuel injection device for vehicles will be explained. In recent years, reduction of CO2 emission and purification of exhaust gases have been promoted in an automotive industry to improve environment.
In particular, a diesel engine has undergone fuel injection pressure increase, multiplication of fuel injection, etc. to the above problems. Therefore, an electromagnetic valve (valve using an electromagnetic actuator) is required to have a quick response property. To achieve the quick response property, it is proposed that a stator core affecting the response property uses SMC that is formed by solidifying iron powder and resin powder. (For example, refer to Patent Document 1)
[Patent Document 1] JP-2001-065319-A.
Meanwhile, in recent years, to increase a response speed, a study that aims at increasing a magnetism property of an armature has been developed. As a means for increasing the magnetism property of the armature, a technology (not known technology) where a shaft as well as a moving core is formed of a ferromagnetic material for enhancing a suction force to the stator core has been developed. Further, a technology where the magnetism property of the armature is increased by using silicon steel or the like as a magnetic material constituting the moving core has been developed.
Consequently, a stator core is required to be in response to an armature excelling in a magnetism property. It is known that, as the SMC decreases in the content ratio of a resin, the SMC increases in a magnetic flux density and in a static suction force. However, as the resin content is decreased, a core loss that affects a dynamic suction force is eventually increased. Therefore, when the SMC is used for the stator core and the resin content is thereby decreased, the magnetic flux density is increased but a response property is deteriorated due to increase of a core loss. Therefore, an electromagnetic actuator having a quick response cannot be provided.